The invention relates to an epitaxial facility for applying semiconductor layers to semiconductor wafers in accordance with the epitaxial process.
With this type of facility or plant, as is generally known, flawless layers of pure silicon, for example, in perfect crystalline array and/or alternatively silicon layers with p-type or n-type conductivity can be applied epitaxially to a suitable substrate, in this case silicon. Such layers form, so to speak, the skeleton of highly integrated circuits. The basic materials used for these perfect crystalline layers are so-called high-purity, and in this case silicon-containing, processing gases, to which traces of p- or n-type doping agents may be added, such as arsenic compounds or phosphorus compounds. The silicon and dopants are deposited on the surface of wafers in the reaction chamber by means of the CVD method. The wafers are inserted in indentations of the support made of graphite coated with silicon carbide, which is heated to a temperature of approximately 1050.degree. C. The support is also referred to as a susceptor. The wafers are thin plates, sliced parallel to the lattice plane of a single crystal of silicon, which have a perfect surface structure whose grid precisely matches the lattice constant. This surface structure forces the silicon atoms precipitated out of the gas phase onto the wafer into the perfect crystalline order required for making semiconductor layers.
The process which has just been briefly outlined for the manufacture of semiconductor starting material by means of gas-phase epitaxy requires highly advanced technology both for heating of the wafer support and for controlling the flow of the processing and scavenging gases. It will be readily understood that the charging and discharging of the wafer support with its sensitive, thin wafers, which take place outside of the reaction chamber, must be carried out under conditions of highly purified air in a specially prepared space in the epitaxial facility. The most recent developments in this area are directed toward handling the wafers and loading the wafer support into the reaction chamber by remote control, without any direct intervention by operators.
To be sure, known plants of the type mentioned above for carrying out gas-phase epitaxy have already been successfully set up for the manufacture of semiconductor starting material; nevertheless, they can still be improved in many respects. Thus, the efficiency of the hitherto used induction heating systems and their tolerability for operating personnel both need improvement. With respect to the remote control of the epitaxial facility mentioned above, improvements still remain to be made in the areas of user friendliness, fully automatic charging and discharging of wafer supports and control routines whereby malfunctions arising in the course of processing can be dealt with. Of primary concern here are the safety of operating personnel in the event of malfunctions and the protection of wafers that are already partially coated.
The most pressing problem still to be solved in gas-phase epitaxy under industrial mass-production conditions, however, relates to the ever increasing requirements in terms of coating quality, which still leaves something to be desired in the case of known plants of the initially mentioned type, due to undesirable particles that are either present in the facility or produced during the process of epitaxial growth. One of the chief problems here is that these unwanted foreign particles can get onto the surface of the wafer and thus interfere with the desired crystalline arrangement as epitaxial layers form.